Complex regional pain syndrome (CRPS) (formerly called reflex sympathetic dystrophy, or RSD) is a condition of severe localized pain.

A person with CRPS often has had a major stressful event like trauma, infection, sprain, emotional stress, surgery or a similar event that is very hard on the body.

The body's nervous system reacts by causing the body to keep sending pain signals to the brain. The brain then interprets these signals as ongoing injury even though the original injury might be completely healed. Most people have pain in their arms or legs but rarely other body parts can be affected.